Alternating electric current rectifier



June 1948- L. E. THOMPSON r 2,444,385

ALTERNATING ELECTRIC CURREKT RECTIFIER Filed Jan. 24, 1946 Bare Plafe I IN VENTOR LemlzEzmeyzT/zampron HIS ATTORNEY Patented June 29,1948

UNITED sTA Es PATENT orrics Appllcation January 24, 1946, Serial No. 643,091

. In Great Britain Jul! 6, 1945 2 Claims. (Cl. 175-366) 1 This invention relates to alternating electric current rectifiers of the dry surface contact type. and has for its object to provide improved arrangements for protecting a rectifier of this character from surrounding atmospheric or other conditions so as to be reliable and durable in service.

In rectifiers of this type it is very necessary to prevent the access of water or moist air to the rectifying or contact electrode surface and special precautions in this respect have to be taken in rectifiers for service in tropical climates or other similar atmospheric conditions as otherwise the rectifiers soon deterioriate or become completely inoperative.

It is found by experience that the usual protection of a coating of paint or varnish is not permanently effective for this purpose, and although the cooling and. spacing element usually provided in contact with the counter or contact electrode is to a considerable extent effective in protecting the surface of the rectifier, moisture is still apt to enter between the electrode'and the rectifying layer at the edges thereof while extension of this cooling element up to or beyond the edges of the electrode is liable to cause a similar ring 5 is similarly placed against the contact electrode at its inner edge. The two' insulatmg bands and the intervening portion of the contact electrode which is not covered by the insulating strips are then provided with a layer of non-porous metal preferably applied by spraying as shown at 8. This layer of metal in combination with the insulating strips 4 and 5 acts to seal the electrode 3 against the access of moisture and thus serves as an effective means for protecting the rectifier when assembled in a stack against surrounding atmospheric or other conditions. After the rectifier has been assembled in a stack, the stack as a whole may be painted, in which event the paint will seal any opening which may exist between the base plate and the opposite exposed portion of the insulating strip 4.

short circuit between the counteror contact electrode and the base plate to which the selenium or other rectifying layer is applied.

In one form of the invention as applied to a rectifier of the selenium type a continuous relatively thin strip or band of insulating material is applied to each edge of the coated base plate so as to overlap the adjacent edge of the contactelectrode, and a layer of non-porous metal or alloy is applied to the element so as to cover tionalview showing one form of rectifier element constructed in accordance with my invention.

Referring to the drawing, the rectifier element I here shown is of the selenium type and comprises a suitable base plate I in the form of a circular washer provided on one side with a layer 2 of selenium the outer surface of which-is covered, except for a small annular area at its inner and outer edges, with a counter or contact electrode 3. A relatively thin ring or band of insulating material 4 is placed against the contact electrode 3 at its. outer edge in a manner to overlap the adjacent edge of the contact electrode and a Theinvention mayevidently also be applied to ,a rectifier of the copper oxide type for the purpose of preventing the access of moisture to the contact electrode which is utilized to establish electrical connection with the oxide layer,

and in thes and other respects the invention is not limited to the particular arrangement above described by way of example.

Although I have herein shown and described only one form of electrical rectifier embodying my invention, it is understood that various changes and modifications may be made therein of suitable conducting material is applied, said member having an annular uncoated area at its edge. a thin band of insulating material applied to said element so as to overlap the edge of said contact layer, whereby an annular opening is provided between said band of insulating material and the uncoated portion of said member for the reception of a paint seal, and a layer of nonporous metal or alloy applied by spraying and covering the central portion of the contact layer and the band of insulating material.

2. In. combination with a rectifier element comprising a metal washer coated on one face with a selenium composition to which a-contact layer of suitable conducting material is applied, said washer having an annular uncoated area at its outer and inner edges, a relatively thin band of insulating material applied to each edge of said 2,444,885 3 element so as to overlap the inner and outer REFERENCES CITED edges of'said contact layer. whereby annular openings are provided at each edge of said washer 2; ifig gggg are of record m the for the reception oi a paint seal, and a. layer oi non-porous metal or y applied b spraying 5 UNITED STATES PATENTS and covering said ban of insulating material Numb N and the portion of said contact layer between 3 gg 3 '9 said bands to prevent the access of moisture to 3.345.122 Hermann Man 28 1944 said contact layer. v

LESLIE THOMPSON. I 

